The present invention is directed to finely structurable resist systems for dry development processes. A latent image is produced in a light-sensitive photoresist layer by imaging exposure and the photoresist layer is specifically chemically modified, to increase its etching resistance to a dry etching process, by treatment with an agent. The present invention is also directed to a method for structuring with dry development.
In the micro-electronics industry, photoresists are used to create components, for example, to manufacture semiconductor components. Photoresists are indispensable for producing, for example, integrated circuits or memory modules. The photoresist functions to allow the definition and production of structures in a photolithographic manner. To this end, a prescribed structure is transferred from a mask to a substrate, for example, a wafer, utilizing optical methods.
The transfer of the structure is accomplished with an auxiliary layer of photoresist. The photoresist being designationally chemically modified based on the exposure. Because of the different chemical behaviors of exposed and unexposed regions, it is possible to develop this "picture". This development can be achieved either through a wet-chemical method or a dry method.
Many recent developments in micro-electronics have been accompanied by an increase in the packing density. This has resilted in the requirement that the structures are smaller. The requirement of smaller structures has placed increased demands on the processes for structure generation. Smaller and smaller structures must be generated, as a result thereof higher resolutions and higher contrasts of the photoresist systems used are required.
In order to meet the demands placed on resist systems, due to the miniaturization of microelectronic components, the resist systems, the apparatus, and the methods used must meet new requirements. Not only do the resist systems influence the resultant structures, the properties of the steppers or, of the stepper lens used for the exposure, also have a great influence on the quality of the structure transfer. The wavelength is specifically related to the stepper and lens, this relationship thus limiting the maximum obtainable resolution. According to the equations: ##EQU1## the smallest resolved structural size (critical dimension CD), as well as, the depth of focus (DOF), are proportional to the wavelength of the light used. CD is also indirectly proportional to the numerical aperture (Na) of the lens used. DOF is also indirectly proportional to the square of the numerical aperture (NA) of the lens used. By reducing the exposure wavelength, further improvements in the structure resolution can thus be achieved.
Wet-developing single-layer resists are known. These, for example, can be composed of a basic polymer and a photoactive component. An example of such a system, includes novolak resins as the basic polymer and quinone azides as the photo-active constituent.
Although these single-layer systems have heretofore satisfied the demands and requirements of photolithography, they do not satisfy the new demands placed on such systems due to the miniaturization of electronic components, for example, structuring with excimer laser steppers in the deep ultraviolet (DUV) range for producing resist structures below 0.5 .mu.m having vertical side walls given high resist thickness. Inadequate resolutions are obtained with known systems given a substrate topography that is increasingly stepped or given highly reflective substrates.
Because the depth of focus becomes smaller given a shorter exposure wavelength and a high numerical aperture for generating extremely small structures, it is extremely difficult given wet-developing single-layer resists to achieve a higher resolution. This is due to the relatively thick resist layers and unavoidable fluctuations in layer thicknesses (over steps on a substrate). These wet-developing single-layer systems are also unsuitable for structuring with DUV light (for example, at 248 nm) due to the high absorption of the light by the novolaks.
In an attempt to alleviate the aforementioned problems of wet-developing single-layer resists, bilayer systems have been developed. These bilayer systems are, however, more complicated. In a bilayer system only an upper thin layer is exposed and structured. The structures produced in such a manner are ultimately transferred into a lower layer(s), the layer that is structured first serves as a contact mask. Depending on the system, a wet development, a dry development (O.sub.2 /RIE), or a combination of the two methods can be used.
Dry-developing single-layer systems are known and are typically less complex than bilayer systems, but, in part, exhibit the advantages of such systems. In such a system, a latent image is first produced in a resist layer by exposure and is subsequently chemically modified by specific chemical treatment exclusively in the exposed or unexposed regions. Through the chemical treatment an etching resistance is created. For example, an etching resistance to oxygen plasma in dry development, can thus be produced by treatment with an organic metal compound, for example, an organosilicon compound. A "bilayer effect" is achieved in that the chemical modification only proceeds in surface-proximate regions and the structure is transferred onto the regions lying therebelow based on anisotropic development.
U.S. Pat. No. 4,552,833 discloses such a method. A resist layer, composed of t-butoxy carbonyl oxystyrol and a photo-active constituent is exposed in a structuring manner with ultraviolet light. The resist layer is subsequently treated with gaseous hexamethyl disilazane at 85.degree. C. in a vacuum furnace. Because of the silylization of the exposed regions of the resist surface that thereby occurs, high-resolution structures are obtained by subsequent "developing" in an oxygen plasma.
European Patent Application No. EP-A 0 13 61 30, discloses a resolution of 0.5 .mu.m, obtained after exposure of a resist based on acrylate by electron beams, treatment with diborane gas at 40.degree. C., and a subsequent dry development.
EP-A 0184567 and EP-A 0248779 disclose a silylization with hexamethyl disilazane or chlorosilanes.
Similar results are obtained with commercial resists and silicon tetrachloride as a treatment reagent.
All of the above examples of dry-developing single-layer resists, however, have various disadvantages. For example, in all the methods, moisture-sensitive, corrosive or toxic gases or liquids are utilized. Accordingly, special, evacuatable apparatus are required. Moreover, the methods have a long duration. Furthermore, the methods must be performed at an elevated temperature. Still further, process control and reproducibility are critical because of a number of process parameters.